The present invention relates to a method of processing an image signal for processing an image by sharpening or smoothing a recorded image in a picture scanning and recording apparatus, such as a scanner, a facsimile apparatus, and the like.
In the first place, with reference to FIG. 1, an example of a picture scanning and recording apparatus, to which the present invention can be applied, is briefly explained.
FIG. 1 shows the construction of an apparatus for reading and recording an original. In FIG. 1, a recording and reading light source 1 (an Ar laser) emits randomly-polarized light beams. A light beam from the laser light source 1 is separated into a s-polarized recording light beam B.sub.1 and a p-polarized reading light beam B.sub.2 by a beam splitter 2. The recording beam B.sub.1 is passed through an optical modulator 3, and thereafter is combined with the reading beam B.sub.2 by a half-mirror 4. The combined beam is sent to a galvanometer-mirror 5 which is part of a scanning optical system, and is converted into one-dimensional scanning light by the galvanometer-mirror. A subsequent light splitting system 6 once again splits the incident light into a recording beam B.sub.1 and a reading beam B.sub.2. The recording beam B.sub.1 is sent to a recording unit 7 to record on a recording member therein.
The reading beam B.sub.2, on the other hand, is directed to a manuscript 8 for scanning the surface of the manuscript 8. This scanning direction is a main scanning direction.
The manuscript 8 is conveyed in the direction shown by an arrow perpendicular to the scanning direction by a suitable means. This conveying direction of the manuscript 8 is a sub-scanning direction.
Therefore, the scanning beam scans the original picture two-dimensionally in the main and sub-scanning directions. By this scanning, an image signal is obtained by a light receiving system including an optical fiber 9 and a photoelectric conversion element 10 arranged to receive reflected light or transmitted light, and the thus obtained image signal is amplified by an amplifier 11 and supplied to a control circuit 20.
At the light splitting system 6, a part of the reading beam B.sub.2 is taken out and sent to a grating member 12. The light passing through the member 12 is converted into an electric signal by a photoelectric converter 13. The electric signal is further amplified by an amplifier 14, so as to take out a grating signal synchronized with manuscript scanning, and the grating signal is supplied to an I/O interface 21 provided in the control circuit 20.
The I/O interface 21 generates clock signals based on the grating signal, supplies the clock signals to a driving circuit 15 of the galvanometer-mirror 5, and supplies them to a first signal processing circuit 22, a line memory unit 23, a second signal processing circuit 24, and a dot image forming device 25 which are provided within the control circuit 20. In addition, the interface 21 and these circuits 22-25 are connected to a central processing unit 27 through a bus 26, so that each kind of control is carried out by an instruction from the central processing unit 27.
The image signal supplied to the control circuit 20 is A/D converted, gradation converted and shading corrected at the first signal processing circuit 22, and thereafter stored in the line memory unit 23. An image signal read-out from the line memory unit 23 is supplied to the second signal processing circuit 24, in which image sharpness is corrected by using a method which will be described later. The output of the signal processing circuit 24 is supplied to the dot image forming device 25 to form a dot image signal. This dot image signal is supplied to a driver circuit 16 for the optical modulator 3. In response to the dot image signal, a modulated signal is supplied to the optical modulator 3 from the optical modulator driver circuit 16 so as to modulate the recording beam B.sub.1 supplied from the laser light source 1. Consequently, image information having corrected sharpness is recorded in the recording member in the recording unit 7.
A method of processing sharpness performed in such an image scanning and recording apparatus is carried out by the line memory unit 23 and the second signal processing circuit 24. There is set within the line memory unit 23 a predetermined n row and n column portion of an image matrix (hereinafter referred to as "window") as a subject to be processed with respect to two-dimensionally aligned image signals. A correction amount S to the image information at the central position within the window is for example calculated by the following equation: EQU S=n.sup.2 a.sub.mm -(a.sub.11 +a.sub.12 . . . +a.sub.1n +a.sub.21 + . . . +a.sub.nn) (1)
where
m=(n+1)/2 PA0 a.sub.mm =pixel information at the central picture element PA0 a.sub.11 -a.sub.nn =pixel information of each picture element within the window
Based on this calculation, all of the image information a.sub.11 -a.sub.nn of the n.times.n picture elements within the window are recorded in the line memories of the line memory unit 23. The image information is successively read out, and the term (a.sub.11 +a.sub.12 + . . . +a.sub.1n +a.sub.21 + . . . +a.sub.nn) of equation (1) is calculated first. Then, the correction amount S is obtained by computer processing on the basis of equation (1), and the central picture signal of the original picture is corrected by the correction amount S.
However, as is well-known, since the image signal obtained by two-dimensionally scanning the manuscript 8 is arranged in time series, the above conventional method cannot be used to calculate the term (a.sub.11 +a.sub.12 + . . . +a.sub.1n +a.sub.21 + . . . +a.sub.nn) until the pixel information for all lines in the determined window have been successively written in each line memory portion corresponding thereto. It is further impossible for the pixel information to be simultaneously written into and read out from the line memory, so that the method of carrying out an arithmetic process in accordance with equation (1) is performed after pixel information of all pictures elements in the window are written in the line memories as in the above-described conventional method. As a result, the arithmetic process requires a long time, so that it is impossible to achieve a high speed image process. Moreover, noise contained in the image signal used for the operation in equation (1) or errors at the time of A/D conversion cause an error in the processed image signal which is finally obtained so that the desired image signal process cannot be attained.